Inside Earth
FES
Name____________________________ Date____________
Learning Goals
• Compare and describe each of Earth’s layers.
• Compare some of the ways geologists learn about Earth’s interior. • Define oceanic and continental crust and the lithosphere. • Describe heat is transferred by convection in the mantle.
• Compare the two parts of the core and describe how they are different from each other.
Vocabulary
• asthenosphere: The layer of the upper mantle that lies below the lithosphere that is solid, but
soft and flexible
• convection cell: transfer of heat by the upward movement of warm, less dense material and
sinking of cooler, denser material
• continental crust: thicker and less dense layer of the Earth’s crust
• core: innermost part of the planet; composed of a liquid outer core and hotter, solid inner core
• crust: rocky, outer surface of the Earth lying on top of the mantle
• lithosphere: crust and upper mantle that combined, make up the rigid out part of Earth
• mantle: thick layer of the Earth between the crust and outer core.
• meteorite: rock or debris from space that crashed onto the surface of the Earth
• oceanic crust: thinner but denser layer of the Earth’s crust
• plate tectonics: The theory that the Earth’s lithosphere is broken into plates (pieces) that move
over the asthenosphere
• seismic waves: waves that travel through the Earth as a result of earthquakes, volcanic
eruptions or explosions
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Introduction
From outside to inside, Earth is divided into crust, mantle, and core. Each has a different
chemical makeup. Earth can also be divided into layers with different properties. The two most
important are lithosphere and asthenosphere.
How Do We Know About Earth’s Interior? If someone told you to figure out what is
inside Earth, what would you do? How could you figure out what is inside our planet? How do
scientists figure it out? Seismic Waves
Geologists study earthquake waves to “see” Earth’s interior. Waves of energy radiate out from
an earthquake’s focus or starting point. These are called seismic waves (Figure 1.1). Seismic
waves change speed as they move through different materials. This causes them to bend. Some
seismic waves do not travel through liquids or gases. Scientists use all of this information to
understand what makes up the Earth’s interior.
Meteorites
Scientists study meteorites to learn about Earth’s interior. Meteorites formed in the early solar
system. These objects represent early solar system materials. Some meteorites are made of iron
and nickel. They are thought to be very similar to Earth’s core (Figure 1.2). An iron meteorite is
the closest thing to a sample of the core that scientists can hold in their hands!
FIGURE 1.1
The properties of seismic waves allow scientists to understand the composition of Earth’s interior.
FIGURE 1.2
The Willamette Meteorite is a metallic meteorite that was found in Oregon.
Crust
The crust, mantle, and core differ from each other in chemical composition. It’s understandable
that scientists know the most about the crust, and less about deeper layers (Figure 1.3). Earth’s
crust is a thin, brittle outer shell. The crust is made of rock. This layer is thinner under the oceans
and much thicker in mountain ranges.
There are two kinds of crust. Oceanic crust is made of basalt lavas that flow onto the seafloor.
Oceanic crust is relatively thin, between 5 to 12 kilometers (3 – 8 miles) thick. The rocks of the
oceanic crust are denser (3.0 g/cm3) than the rocks that make up the continents. Thick layers of
mud cover much of the ocean floor.
FIGURE 1.3
A cross-section of Earth showing the following layers: (1) continental crust, (2) oceanic crust, (3)
upper mantle, (4) lower mantle, (5) outer core, (6) inner core.
Continental Crust
Continental crust is much thicker than oceanic crust. It is 35 kilometers (22 miles) thick on
average, but it varies a lot. Continental crust is made up of many different rocks. All three major
rock types —igneous, metamorphic, and sedimentary —are found in the crust. On average,
continental crust is much less dense (2.7 g/cm3) than oceanic crust. Since it is less dense, it rises
higher above the mantle than oceanic crust.
Mantle
Beneath the crust is the mantle. The mantle is made of hot, solid rock. Through the process of
conduction, heat flows from warmer objects to cooler objects (Figure 1.4). The lower mantle is
heated directly by conduction from the core.
Hot lower mantle material rises upwards (Figure 1.5). As it rises, it cools. At the top of the
mantle it moves horizontally. Over time it becomes cool and dense enough that it sinks. Back at
the bottom of the mantle, it travels horizontally. Eventually the material gets to the location
where warm mantle material is rising. The rising and sinking of warm and cooler material is
convection. The motion described creates a convection cell.
Core
The dense, iron core forms the center of the Earth. Scientists know that the core is metal from
studying metallic meteorites and the Earth’s density. Seismic waves show that the outer core is
liquid, while the inner core is solid.
FIGURE 1.4
In the process of conduction, heat flows from warmer objects to cooler objects.
FIGURE 1.5
The rising and sinking of mantle material of different temperatures and densities creates a
convection cell.
Movement within Earth’s outer liquid iron core creates Earth’s magnetic field. Convection
currents form in the outer core because the even hotter inner core heats the base of the outer core.
Lithosphere and Asthenosphere
The lithosphere is composed of the crust and the uppermost mantle. This layer is rigid, solid, and
brittle. It is easily cracked or broken.
Below the lithosphere is the asthenosphere. The asthenosphere is in the upper mantle. This layer
is solid, but it can flow and bend. A solid that can flow is like silly putty.
Lesson Summary
• The Earth is made of three layers with different composition: the crust, mantle, and core.
• The lithosphere is made of the rigid, brittle, solid crust and uppermost mantle.
• Beneath the lithosphere, the asthenosphere is solid rock that can flow.
• The hot core warms the base of the mantle, which creates convection currents in the mantle.
Review Questions
1. Describe two ways that scientists learn about what makes up the Earth’s interior.
2. What type of rock makes up the oceanic crust?
3. What types of rock make up the continental crust?
4. How does the density of oceanic crust compare with the density of continental crust?
5. How does the thickness of oceanic crust compare with continental crust?
6. Describe the properties of the lithosphere and asthenosphere.
7. When you put your hand near a pan above a pan filled with boiling water, does your hand
warm up because of convection or conduction?
If you touch the pan, does your hand warm up because of convection or conduction?
8. List two reasons that scientists know that the outer core is liquid.
9. Suppose the Earth’s interior contains a large amount of lead. The density of lead is 11.3
g/cm3. Would the lead be more likely to be found in the crust, mantle or core?
10. If sediments fall onto the seafloor over time, what can sediment thickness tell scientists
about the age of the seafloor in different regions?
11. Which layer of the Earth is the hottest?
12. How might convection cells in the mantle affect the movement of tectonic plates?